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int parse_message(struct nlmsghdr *hdr)
{
/*
* The policy defines two attributes: a 32 bit integer and a container
* for nested attributes.
*/
struct nla_policy attr_policy[] = {
[ATTR_FOO] = { .type = NLA_U32 },
[ATTR_BAR] = { .type = NLA_NESTED },
};
struct nlattr *attrs[ATTR_MAX+1];
int err;
/*
* The nlmsg_parse() function will make sure that the message contains
* enough payload to hold the header (struct my_hdr), validates any
* attributes attached to the messages and stores a pointer to each
* attribute in the attrs[] array accessable by attribute type.
*/
if ((err = nlmsg_parse(hdr, sizeof(struct my_hdr), attrs, ATTR_MAX,
attr_policy)) < 0)
goto errout;
if (attrs[ATTR_FOO]) {
/*
* It is safe to directly access the attribute payload without
* any further checks since nlmsg_parse() enforced the policy.
*/
uint32_t foo = nla_get_u32(attrs[ATTR_FOO]);
}
if (attrs[ATTR_BAR]) {
struct *nested[NESTED_MAX+1];
/*
* Attributes nested in a container can be parsed the same way
* as top level attributes.
*/
err = nla_parse_nested(nested, NESTED_MAX, attrs[ATTR_BAR],
nested_policy);
if (err < 0)
goto errout;
// Process nested attributes here.
}
err = 0;
errout:
return err;
}
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